Method of dead banking blast furnaces



Patented Nov. 17, 1942 OFFICE METHOD OF DEAD BANKING BLAST FURNACES Lawrence E. Riddle, Duquesne, Pa.

No Drawing. Application February 13, 1941, Serial No. 378,819

4 Claims.

This invention relates to a method of dead banking a blast furnace, and relates more particularly to a method which effects economies in time and labor in the respect that the necessity for the service of men to watch the condition of the furnace, including the drafts, circulating cooling Waters, etc., during the period of banking is entirely dispensed with and further economies of time, labor and materials are effected, particularly where the combustion within the furnace has become extinguished and it is necessary to refire a blast furnace which has been dead banked. From the latter aspect, a saving of time and labor isleffected by employment of the improved method, particularly when utilized in connection with my improved method of refiring by dispensing with the necessity of at least two steps heretofore found necessary; (1st) by eliminating that step comprising the removal from the furnace of the entire residue of the unburned burden including the ash, unburned fuel, limestone, slag, metal, and the like, and (2nd) by eliminating that step of providing a charge of readily ignitible and. rapidly combustible wood and charcoal adjacent the tuyres and in the hearth portion to facilitate preliminary kindling and rapid rate of Referring further to the first step mentioned above, it is common practice, in the case of furnaces banked in the manner of the prior art for long periods of time during which an appreciable portion of the extra coke charge is burned, to rabble out, the furnace. This practice required that the furnace be blown in, as in the case of a new furnace, 'with a fresh charge of coke, limestone, ore and the like. By the procedure of my invention, all these cos ly operations are eliminated because the condition of the materials in the furnace at the time of banking is preserved throughout the entire period during which the furnace is banked. I

The improved method of banking is intended to be practiced particularly in connection with my improved'method of firing a new furnace, or refiring a furnace which has been banked but in which combustion has terminated, which improved process of firing constitutes the subject matter of a co-pendin'g application, although it may have application in this art, independent thereof. Stated generally, such improved method of firing a furnace consists in supplying an atmosphere of substantially undiluted oxygen, together with a suitable source of ignition or kindling temperature, as by kindling torches such as an ignited oxygen lance, oxyacety ne, or the like,

or remove, the entire contents of.

combustion of the coke charge.

at certain controlled combustion zones within a fuel bed of coke. For further details of the method of refiring, reference is made to my copending application, entitled improvement in Method of firing a blast furnace, Serial No. 359,797, filed October 4, 1940.

For a better understanding of the present improved method of banking, it might be well to make more detailed reference to the practice of banking blast furnaces as commonly followed in the prior art. The normal life of a blast furnace lining is from four to six years. This period is usually designated as a campaign period of the furnace. It frequently happens that during a campaign, the demand for the product of the furnace is not suflicient to warrant normal continuous operation of the furnace by periodic tapping and charging at full, or even reduced, capacity. Other conditions, such as strikes, may prevent normal continuous furnace operations.

In such instances it has been necessary to bank the furnace with the expectation of resuming blowing operations within some indefinite unknown period of time, which may be a few Weeks or a few months. method usually followed, which might be termed a live banking method in contradistinction to the present method which might be termed an accelerated dead banking method, the furnace is filled with a burden richer in coke than normal; the blowing operation is stopped; the blow pipes and tuyeres at the bottom of the furnace are removed; and the openings are sealed. Every precaution is taken to retain the heat stored in the furnace and, at the same time, to limit the combustion of the coke to a minimum, just sufficient to prevent the fire from being extinguished.

If the banked furnace is one of several connected to a'common system of gas mains, and one or more of such other furnaces is still in blast so as to maintain a difference in gas pressure conductive to a draft, the connections to the top of the live banked furnace are broken or interrupted temporarily to prevent any draft to the banked furnace which otherwise might stimulate combustion therein. Under such prior art conditions of live banking, active operation of a furnace banked for a short period may be resumed by making the necessary connections and installing the tuyres and the air blast, provided the combustion has not been completely terminated.

Even under the most favorable conditions of banking, and when combustion has been reduced to a smouldering minimum and there maintained, a certain amount of fuel is consumed and there is a certain amount of ash formed, and it is fur- In the prior art banking ther necessary to keep the water circulating through the bronze bosh plates and tuyere coolers in order to protect the same from being damaged or destroyed by becoming warped oriburned out. As above indicated, if the banking period has been extended for more than about five weeks, under which conditions there has been considerable ash formation with some coke still ignited; or if the furnace has not been carefully supervised; or if a sudden chilling has occurred, as from water leaks in cooling plates, to a point where combustion has been inadvertently terminated, it is not possible to resume normal active or capacity operailon of the furnace by making the usual necessary connections and restoring the tuyere and blast furnace connections. as above indicated. Under such conditions, it has been the prior practice to entirely clean out the furnace, and to fill in another charge as in starting a new furnace, which charge has usually included necessarily the use of wood and charcoal as kindling and easily ignitible and combustible fuels to facilitate initial rapid rate of combustion in refiring the fresh charge of the furnace. These steps of cleaning out from the furnace the residue of are in various stages 'of reduction-slag, limestone, coke in various stages of combustion, ash, and clinker-4s a laborious and tedious operation which, together with the recharging operation, consumes much time which may amount to as much as six days.

One of the objects of this invention isto provide a novel method of dead banking blast furnaces which will overcome certain of the obilections and difficulties encountered in the prior art method of live banking, as above referred to. by employing a dead banking method of rapidly and completelylasphyxiating the combustible charge and as rapidly as possible effecting a reduction of temperatures below the ignition or kindling point of the coke, which procedure eliminates a number of the steps in the method of live banking that heretofore have been practiced and thought to be essential.

A further object is to provide a method of banking a blast furnace by the practice of which major economies in time, labor, fuel and water consumption and other materials are effected by dispensing with certain steps in the methods of banking and refiring heretofore followed and thought to be necessary. v

More specifically stated, one of the further objects of this invention is to provide a method of banking a furnace which will permit of immediate resumption in the operation of a bankedfurnace, irrespective of the period of time during which the operation of the furnace has been discontinued, and this without the usual trouble and expense incident to the necessary removal of the entire contents and subsequent recharging of the furnace. This is accomplished by inby an endothermic .cooling action in which ed, by developing and. maintaining for a sumcientcombustion asphyxiating period (in which the coke is reduced to a temperature below the kindling point) a slight internal pressure by the use of an anti-combustion supporting gaseous atmosphere having substantially no free oxygen therein, uing combustion of the coke. Such an atmosphere within the furnace may include any one or any mixture of what are normally (in the presence of free uncombined oxygen) to be noncombustible or combustible gases or vapors, as long as they are oxygen free; that is, they should include no uncombined oxygen capable of supporting combustion. The gases may, however, be chemically active in the sense that they may react with the hot coke, ore,or limestone, preferably in such a manner as to be accompanied or heat absorbing type of reaction, although this latter, while preferable, is .not essential. One advantage in employing a gas or mixture of different gases capable of chemically reacting with the various ingredients of the heated furnace charge, when accompanied by an endothermic type of reaction, is that it contributes to bring about a desirable accelerated the temperature of'the furnace and its contents is reduced at a relatively rapid rate to a point below the kindling temperature of the coke. In this way, further continuing combustion of the coke as fuel is precluded, and combustion is terminated with a minimum of ash formation during the dead banked period. This is a highly desirable and advantageous condition as it effects economy'of fuel and precludes any substantial settling or dropping of the residue dead banked charge upon I resumption of normal furnace operation follow-- ing refiring in accordance with my improved method of starting. an extinguished blast furnace' without the necessity of cleaning it out. If, after the fire within the furnace has been extinguished, any air should leak into the furnace, such air would mingle or possibly react with the gases of the class above referred to rather than react with the coke, by such time have been reduced to a temperature below its ignition or kindling point.

An additional feature of in employing the dead banking step in the combination method is one which experience has shown to facilitate and accelerate the quick starting kindling-like operation and the rapid:

" and uniform distribution of heat. in the refirlng:

tentionally and designedly maintaining and pre- .dead banked, without the formation of any further ash during the banking period, irrespective of its length of time. A further object is to provide a method of dead banking a blast furnace in which, during 3 the banking period, infiltration of outside combustion-supporting atmospheric air within the blast furnace is minimized, if not precluded, during the initial periodof the dead dunking methstep of the method. This feature is made possible by reason of the porous character and absorptive properties of the coke and the liquid character of the metal in the general zone of the hearth, bosh, and lower stack portion of the furnace, and in the zone adjacent the tuyeres, through which the ignited oxygen lan'ces or similar means are inserted in refiring the dead banked residue charge. It has been observed that in the practice of the dead banking step the liquid metal which has solidified in the pores of the coke on cooling. It has been found that the absorbed iron within the porous coke appears to have the effect of intensifying the heat of combustion of the coke with undiluted oxygen and of raising the ignition temperature to a point higher than if there were no liquid iron in the pores of the coke. During the cooling operation when the furnace is being dead banked, the effect of this would be to more quickly bri such as would support furthercontinwhich would advantage obtained of the method, the porous coke has absorbed the coke below its ignition temperature so that any air which might later come in would mingle or combine with whatever gasv is being used rather than to react with the coke. On the other hand, on refiring the residue of the dead banked charge in the furnace, the solidified finely divided particles of iron absorbed by and with the porous coke appear to facilitate a more uniform distribution and transfer of heat, which facilitates ignition and accelerates the rate of coke combustion in the intense heat within the influence of the ignited oxygen lance. This phenomenon may in part be explained by the relatively poor thermal conductivity of the carbonaceous material and confined gas pockets of the porous coke, which serve as relatively poor thermal conductive properties, as compared with the better thermal conductive properties of iron, and also the fact of the wide variation of the specific heat of iron at the different temperatures of 100 degrees C. to 900 degrees C. which varies from between one to over 15,000 per cent, the specific heat of iron being greatest at the higher temperatures. For example, at 100 degrees C. the specificheat of iron is 0.12 cal. per gram per degree centigrade, and at 900 degrees C..it is 18.5 cal. per gram per degree centigrade.

Wth reference to the gases or combination of gases which may be suitable for use in practicing themethod of dead banking the furnace, I preferably use a gas containing a mixture of the following gases in about the proportion indicated:

Per cent Carbon dioxide (CO2) 14 Carbon monoxide (CO) 25 Hydrogen (H2) 2 Nitrogen (N2) 59 Water (vapor steam) (H2O) Small amount The above represents the approximate analysis of a blast furnace gas which was used with success. Such. a blast furnace gas may be most convenient for use, particularly where several furnaces are being/used. As I have used it, the furnace gas was piped from the clean cold gas main and forced into the furnace through one or more of the tuvez'es after the blast was shut off. The exact procedure must, of course, be varied at different furnaces, and to make such variations is within the abilities of skilled operators. Furnace gas thus ntroduced gives effects entirely different from effects of gas forced by back pressure through the top of the furnace.

Other gases which may be employed satisfactorily (of course, in the absence of any free uncombined oxygen) are producer gas (of a composition approximating the blast furnace gas and also including methane (CH4) 2 to 4 per cent; ethylene (C2H4) less than 1 per cent); natural gas a typical natural gas contains 80 to 90 per cent methane (CHO) 3-4 per cent nitrogen (N2); less than 1 per cent carbon dioxide (CO2); no carbon monoxide CO) or free uncombined hydrogen (H2) coke oven gas having as a typical analysis the following approximate composition:

Per cent Methane (CH4) 29 Ethane (CzHe) 1 Ethylene (C2H4) 3 Carbon monoxide (CO) 6 Hydrogen (H2) 57 Nitrogen (N2) Less than 1 Carbon dioxide (CO2) 2 A wide choice of gases, either chemically active or inert (both with respect to the elements within the furnace in the absence of free uncombined oxygen), may be used, depending upon which one or combination of gases is most conveniently available. The extent to which the endothermic v heat absorbing reactions take place for effecting the accelerated cooling action will, of course, vary with the particular gas used and the presence in said gases of the elements capable of chemically reacting with the heated elements in the furnace to bring about such endothermic reactions. .The dead banking method of promptly terminating combustion of the coke may be practiced by the use of certain of the inert asphyxiating gases above noted, (in the absence of free uncombined oxygen) such as nitrogen, even when not accompanied with the endothermic reaction. Such inert gases introduced in the blast furnace, preferably under slight pressure, will serve to arrest further coke combustion and ash formation, and also serve to minimize, if not preclude, infiltration or leakage of atmospheric air Within the furnace. Under the latter conditions, the rate of cooling will be somewhat retarded.

In the practical application of the method 'of ead banking a blast furnace which has received the conventional charge of iron ore, coke, and l'mestone, reference will now be made to an illustrative case in which a blast furnace gas was emloyed as the preferableasphyxiating gas (in the absence of a supply of free uncombined oxygen).

other furnaces were 1 tie] amount Such blast furnace gas was readily available as being operated in the adjacent location.

A most unexpected and unanticipated advantage and result occurred when furnace gas containing a mixture of different gases such as carbon monoxide, carbon dioxide (active at about 900 degrees C. with red hot carbon), hydrogen, nitrogen. and water vapor, was supplied to the combust on zone in the absence of any substanof free oxygen (sufiicient to support combustion) in order to terminate furthercombst on and smother orasphyxiate the fire within the bast furnace. The chemically active gases, in the absence of free oxygen sufllcient to support combustion, not only appeared to rapidly term nate further combustion and smother the fire, but they also brought about reactions which resulted in an accelerated cooling or heat absorbing function fargreater than that which would have been normally expected to have been effective from the physical standpoint, as by heat dssipat on by conduction, convection, or radiation. o bring about or contribute to a more rapid reduction of the temperature below the kindling po nt and thus assure a-more rapid termination of f"rther combust on of fuel and/or the prevention of the further formation of any substantial amount of ash. The precise chemical reac ions and endotherm c effect of the chemically ac" ve asphyxiating gas or combination of gases n the absence of oxygen) at the relatively high temperatures of the coke, ore, and other constitucuts of the charge within the blast furnace are of a c mplex and varied character and may occur at various portions, at different times, and at varying t mperatures throughout the furnace, either s multaneously or in succession, and at varying rates, as the various gases and combinations thereof are brought into intimate contact with he hot c. e 0 e a d lime cha gev slag and metal of the furnace and its different elements existing at temperatures varying from about 500 degr us tuyre openings.

' During the same period while the temperatureis actions, it is possible to formulate a reasonable or basis, consistent with the ob- One phenomenon observed, 1. e.,

explanation, served results.

the relatively rapid darkening and cooling of the red or white hot coke when in an atmospherev lacking in free or atmospheric oxygen but rich in, or having anexcess of, chemically such as carbon monoxide, hydrogen, carbon dioxide, in contact with the various solid and liquid materials in the furnace at temperatures varying from about 500 degrees C. to 1200 degrees 0.. seems to indicate that one or more heat absorbing endothermic reactions take place in blast furnaces in which the burning charge with furnace gas,- sence of or with little ening of the coke from the red heat, it was noticed by observation through the tuyere o'peningsthat hours after the chemically within twenty-four active gas constituents of the furnace gas had been conducted to the combustion zones of the furnace to arrest further ash formation, there was evidence of moisture formation This would be an indirect indication of the cooling of the coke to below such a temperature at which the moisture could react with the hot coke. Further active 88.8%,

burning or combustible charge has been dead banked by asphyxiating the but in the abor no fresh free oxygen supply. In addition to the relatively rapid darklikely heat absorbin some of thereactions ill be r v rsible, adjacent the a w e e reactions are those in which the various oxides of iron such as FeO, 3F820s and F8304 may react with the carbon alone at the relatively high temperatures in the lower part of the furnace to form a certain amount of carbon monoxide.

Specifically, the reactions that take place in the region of the hearth and bosh on the introduction of the asphyxiating gas mixture contain-,

ing considerable carbon dioxide and water vapor,

such as blast furnace gas,

mately as represented by the following reactions:

CO; +C= 2C0 (38,88O cal.)

7 From this reaction it is evident that approxi-- mately 38,880 cals. of heat is absorbed for eachmolecule of C02 contained in the asphyxlating 888- Carbon dioxide may also react with the metallic iron which is found of the furnace, heat conditions in the lower part of the furnace at the time the gas is introduced. These reactions are,

as follows:

Fe+ 002 FeO co (-2,;340 cals.) -97,200 +s5,700 +29,1eo I 0, 400 .(-i,360 cals.) 3ss,soo na270,:300

of the asphyxiating or extinguishing process, still sufficiently high, the iron oxides formed by the two equations above, react with the carbon of absorb heat approxiwith the coke in this part being absorbed with each type of reaction possible under the temperature will react with C and Fe under temperature andpressure prevailing during the.

the coke to absorb heat in accordance with the following two reactions:

Fe O C 3Fe0 CO 270,800 +197,100 +29,l

( 44,540 cals.)

gases, this water the conditions of banking period to absorb 20,792 cals. according to the algebraic sum of the following reactions;

At some 'stage of a long dead banking period the latter reaction may progress to the left absorbing 7,874 cals. of heat, so that the sum total of heat absorbed by these two reactions will then be 36,540 cals.

In considering these reactions it is necessary to keep in mind that the temperature conditions in any specific case of dead banking may extend over a wide range; being possibly as high as 3000 F. at the beginning of the process of asphyxiation and dropping to possibly as low as 500 F. at' the end of a. lb'rig banking period, and that also that in general the extent to which they progress endothermically, will depend upon relative amounts of C02, CO and water vapor'contained in the ex-' peratures at the beginning of the extinguishing process, are ,those involving decomposition of methane in gas mixtures containing this gas,

such as coke oven, natural, or producer gas.

This reaction may be represented as follows:

4 (1+ 2H (2,034 'cals.)

2,034 I a v The only extinguishing gases that may be used which do not give heat nitrogen or mixtures of nitrogen and carbon monoxide. With nitrogen, the compounds likely to be formed under the conditions of asphyxiating a furnace are oxides, ammonia, and cyanogen compounds, some of which have negative and somepositive heats the amounts of heat so that nitrogen may be looked upon as one of the less eflicient extinguishing agents.

At the high temperature of the coke and ore,-

contact reactions may take place between the gases chemically active in theabsence of free oxygen andtli'ehotcoke and ore, and/or directly between the hot carbon and the ore, most of which are endothermic the absence 'of a continuing fresh oxygen supply, further" combustion of' the fuel is precluded. A fairly rapid intemal dissipation of 'the reservoir of heatis effected and accelerated by supplying chemically active gases in the absence of any or a suillcient amount of oxygen to support combnstion, by reason of the heat absorbing endothermic type of reaction with the hot coke and other possible reactable constituents of the hot charge throughout the furnace, including to the water vapor that maybe intro absorbing reactions, are

of formation, but in all cases '1 involvedare relatively small,

in character, so that irithe ore,- fiuxing agents such as limestone, and slag. The; reduction of temperature of the fuel below the. kindling... temperature by best. i t n on r sulting from rapid substantially instantaneous chemical contact endothermic reactions is a preferable method to other physical methods of heat dissipation which are dependent upon the much slower physical'processes of conduction, convection, or radiation, for dissipating the reservoir of heat through the walls of the furnace to the circulating cooling water and the outside atmosphere. In accordance with the usual methods and practices of what might be termed the live banking methods of the prior art, the dissipation of the heat by conduction and convection by blowing atmospheric air through the furnace and out the stack is precluded because that would not result in banking the furnace, but would result in further rapid fuel combustion with I ash formation and thus defeat the real object and purpose desired, i. e., fuel conservation and dead banking for any desired period, after which the dead banked charge may be again lighted without requiring cleaning out. of the dead banked, already partially reduced and refined charge. The fairly rapid termination of combustion, by reduction of the temperature of coke to a point below the kindling or ignition point, is a feature of importance because it is related to facilitation of refiring of the residue of the dead banked charge at the end of the dead banking period by minimizing ash formation, and by minimizing the amount of settling upon refiring the charge.

The accelerated dead banking of the partially reduced charge is also an important factor contributing to the shortened time period in the production of a more uniformly good grade of iron upon the first tapping, after refiring the dead banked charge, than was possible by following prior art methods 'where the old extinguished furnace charge was cleaned out and another fresh charge put in. The practice of the dead banking method enables economies of fuel and cooling water consumption to be effected. Upon termination of further combustion, by providing an atmosphere of inert or active gas in the absence of oxygen which will not support combustion, the formation of any further ash is avoided, irrespective of the length of the banking period. of the methods of live banking as commonly practiced by the prior art. In this respect the present invention stands in striking contrast to the teaching and actual practices of the prior art.

In addition to the economies effected by dispensing with the necessity of burning any fuel during the dead banking period, irrespective of the length thereof, a substantial economy is effected in also tuyre coolers and plates in the walls of the hearth and bosh to prevent warping and burning out of such parts, as required by prior art methods throughout the entire banking period.

In accordance with the present method of dead banking, after a comparatively short period of time within which further combustion has been terminated and the stored heat within the furhas been reduced to a temperature where the various cooling plates are not likely to be damaged, the further circulation of the cooling water may be entirely dispensed with. In the normal operation of the blast furnace, the heat absorbed by the various cooling plates represents about 82 to 94 per cent of the total loss of heat produced by the fuel consumed in the blast furnace. The heat losses in the circulating cooling water during the banking period will not be as great as during the normal operation, but such heat losses during thebanking period, particularly if such banking is for a considerable period of time, perhaps a matter of many weeks, are nevertheless a maintenance factor and require service of supervision.-

As indicating the relative magnitude of the next highest source of heat loss during normal operation, it. might be stated that the shaft losses by radiation are from 1.4 to 7.8 per cent and by convection, 1.6 to 8.7 per cent of the total heat losses. These losses reduced during the banking period, as practiced by the prior art, would also be avoided. In any event, during the banking period the methods of the prior art required the service of a man to watch and supervise the furnace. By the method of dead banking the furnace, all of the above heat losses of fuel and water consumption, together with the necessity of costs of supervision, are eliminated.

When the present method of dead banking is practiced in connection with my improved method of refiring or starting an extinguished .banked blast furnace, it is desirable to remove only any coke, ash, slag, etc., that may be located in or directly in front of the tuyeres, but the residue portion of the burden of coke, limestone, slag, etc., is not removed. The failure or omission to do certain acts and follow certain practices, and employ certain steps might be called negative steps which are directly contrary to prior art they constitute positive, definite and essential factors in the success, teaching, and advantages of the method over prior art.

In order to remove the ash, in following the practice of my refiring method, prior to rekindling and heating the residue of coke or limestone, etc., of the dead banked burden, it has been found satisfactory in practice to apply the air'blast to the tuyeres and blow out all of the readily removable ash and ash-like residue through the tapping hole or cinder notch.

After removal of the ash from the blast furnace, there may be a slight settling of the more solid coke and ore charge from above, dependent on the particular conditions at the time of dead banking. According to the practice and methods of the prior art, the kindling charge of wood and charcoal extends as much as ten feet up the stack to fire the furnace and obtain the initial heat for kindling the burden of coke and ore above. A substantial settling action of the coke, ores, and limestone burden above has ordinarily occurred after the combustion of the kindling portion of the charge. This is another respect in which the practice of the present dead banking method in connection with the method of refiring is contrary to customary prior art practice. In the operation of the blast furnaces, such settling or, as sometimes happens, a failure of the solid charge above to settle through a jamming or wedging of the charge has resulted in hazards which have on occasions resulted in serious loss and damage either to the burden, the furnace lining, the tuyeres, or to the operators through explosive accumulation of gases. Such conditions may also cause a nonuniform layer or zone of combustion which frequently causes any one of the numerous irregularities at times met with in blast furnace operatic some of which have employment of the present of methods of the prior art teaching and practices; but

V itial product obtained been referred to at times as hanging charges," slips, chimneying, scaffolding, "pillaring," "hot spots, and chilling of the molten metal in the hearth, the latter being due to a sudden slipping or settling of a large mass of the relatively cooler ore metal in the crucible.

By providing a method of dead banking and refiring such dead banked furnace, in accordance with the method of the present invention, in which the settling of the main burden would have already occurred, the likelihood of the commence of the above enumerated hazards and irregularities in blast furnace operation are greatly minimized.

It has been found in practice that when the method of the present invention is applied in the reflring of a dead banked furnace in which combustion. has been extinguished, a time saving of approximately six days is effected as compared with prior art methods where the furnace is cleaned out, considering a period from the time of starting to clean out the furnace up to the period in which good iron is obtainable from the furnace.

A comparison of the present method with those of the prior art, with respect to the period from igniting of the kindling charge of prior practice, and actual reflring under this method, up to the time when an initial tappin of good iron maybe obtained, has shown that by employing the residue charge of coke and employing the undiluted source of oxygen to sustain combustion, the production of uniformly good iron on the initial tapping can be obtained in a much shorter period of time than by the practice of prior methods or customary practices wherein the furnace was entirely cleaned out and another blow-in burden employed. By the practice of my invention, 1 have been able to tap good iron from the refired furnace on the -fifst or second tap, 6 to lo hours after relighting or refiring,

- whereas by the methods of the prior art of ing, good iron is seldom obtained before the sixth tap, 24 to 30 hours after relighting or refiring, even though the furnace has been banked for only a short time.

It has also been found that by the employment of the method herein disclosed the likelihood of the production of what is known as "offgrade iron at the first tapping is greatly lessened. in this respect, the practice of the improved method enables an improvement to be: efiected in obtaining a greater uniformity in the grade and character of iron free from contamination which is produced on the initial tapping following the refiring of the furnace, and this in a shorter period of time than by the practice of prior methods. In this respect, the resulting improvement in uniformity of the product on the initial tapping obtained by the practice of this improved method is peculiar'and inherent in this method. The same statement might also be fairly made with respect to the saving in time within which the production of a uniformly good grade of iron is obtained upon initial tapping. Apart from the improvement in the resulting character of the inon the first tapping, the nature of the positive steps employed, resulting in the failure or omission to followcertain steps and customary practices of the prior art, areof such a character that it might be fairly said that the method was doing that from above into the molten suiting ther combustion,

be contrary to accepted customary practices in the art of banking and refiring blast furnaces.

It is difficult and hardly feasible at this time to give a. positive,

improved results in the nature and uniformity of the product initially obtained on first tapping, or a of the saving in time after the initial firing over the prior practices. However, the following might be mentioned in partial explanation as likely factors contributing toward the improved results, and as illustrative examples of the endothermic heat absorbing type of reactions which may occur, refrom reactions of certain gases with certain elements of both the heated coke and ore constituents of the charge.

By employing in the reflring method a residue charge of coke and ore that has been dried out and previously subjected to the high heat of the blast furnace, such residue products, particularly the ore, are in a condition of partial refinement, different portions ofthe ore. being in various states of reduction from that of substantially pure iron to different degrees or conditions of oxidation, including that of ferrous oxide; (FeO) hematit-ferric oxide (F8201) and magnetite (Fe2O4) In this state of partial reduction of the residue charge existing at the time that the furnace is banked in such manner as to preclude furit is perhaps possible that portions of the sponge-like or porous ore within certain zones of the blast furnace which have a ratio of CO/C0a=0.4 and which have been subjected to maximum temperatures of about 450 which was deemed 15 degrees C., may have absorbed certain amounts of free, finely divided carbon into intimate surface contact relation which is well known to stimulate and accelerate chemical reacti0nwhich finely divided carbon may have resulted from a reversible reaction between 2CO@CO2+C::38,880 58,320 Calories 97,200 Calories bustion by the pure oxygen, the first reactions to' occur undoubtedly are those which begin at as low a temperature as 300 degrees C. in which the ferric oxide (F6203) may react with carbon monoxide (CO) in accordance with the following formula, which reaction is exothermic in nature and liberates considerable heat:

2Fe2O3+8CO=7CO2+4Fe+C(+55,920 Cal.) 391,200 Cal.2 33,280 Cal.+'680,400 Cal.

Heat is liberated in both of the above reactions. This would facilitate further reaction with an economy of fuel. Other reduction reactions of the iron ore by carbon alone absorb much heat and are to be avoided during normal operations of a furnace if conditions permit. From the above possible reactions (in dealing with the refiring of a residue charge) it would seem as though the initial combustion of coke in the atmosphere of substantially undiluted oxygen and accepted explanation of these the heats of combustion and exothermic type of reaction therefrom, would be more quickly effective to produce a good uniform grade of iron upon the first tapping than would be the case if the prior art practices were followed, in which an entire blow-in burden were used and diluted oxygen in the air employed as the gas to support combustion. In the latter instance, a great portion of the initial heat would be lost in drying and heating the charge and in heating the inert gases of the air'sc that this of itself would be sufficient to cause a delay in the period within which a uniform good grade of iron might be obtained on the first tapping.

It is understood that instead of one, a plurality of jets supplying the atmosphere of undiluted oxygen, together with ignition torches, such as ignited oxygen lances, oxy-acetylene torches and the like, may be disposed at various positions and depths of penetration of the coke charge and simultaneously fired, if desired, to initially obtain a bed or zone of combustion, uniform in character.

In the above matter, reference has been made to the refiring of a dead banked furnace as a step in the general method of furnace operation, and certain reactions were referred to astypes of exothermic heat-evolving type of thermal reactions which might possibly take place, in an attempt to explain and understand the advantageous and end results obtained and observed,.

and with a view of utilizing control factors for obtaining economical and efficient operation and desired products.

From the above description of my invention, it will be apparent that many modifications of the same may be devised within the scope thereof and all such modifications are contemplated as may fall within the scope of the appended claims.

I claim:

1. The improved method of dead banking a blast furnace without the necessity of including a preparatory damping charge which includes the following steps: terminating the air blast whereby the normal supply of free oxygen from the air to support combustion is removed, and promptly supplying in the combustion chamber in the high temperature zone below the stack adjacent the bosh, where during normal furnace operation temperatures exist above the reaction temperature of carbon dioxide and red hot coke so as normally to preclude the existence of carbon dioxide under such conditions, an atmosphere in- Y cluding a substantial amount of carbon dioxide gas whereby further combustion and ash formation is prevented, said gas reacting chemically with the red hot coke, in the absence of free oxygen, to effect an endothermic heat absorbing reaction to obtain an accelerated cooling of furnace and contents to a temperature below the ignition temperature of the coke.

2. The improved method of dead banking a blast furnace as defined in claim 1 and including the step of supplying clean, cold furnace gas including said carbon dioxide gas initiallylto the lower high temperature portion of the furnace below the stack where normal operating temperatures in excess of about 900 degrees C. prevail, such high temperatures precluding the existence of carbon dioxide in the normal furnace operation.

3. The improved method of dead banking a blast furnace without the necessity of including a preparatory damping charge which includes the following steps: terminating the air blast whereby the normal supply of oxygen from the air to support combustion is removed, and promptly supplying in the lower portion of the furnace shaft, where the normal operating temperatures are above about 900 (3., about the reactive point of carbon dioxide gas in the presence of red hot carbon, an atmosphere including a gas incapable of supporting combustion, in the absence of free oxygen, whereby further combustion and ash formation is precluded, said gas including substantial amounts of carbon dioxide and carbon monoxide, each of said constituent gases being capable of producing endothermic heat absorbing types of reactions with the hot coke, ore and metal constituents of the furnace, to obtain an accelerated cooling of the furnace temperature, to a point below the ignition temperature of the coke, the carbon dioxide constituent of the gas reacting with the carbon at a temperature above about 900 C. being the primary constituent initially producing the major accelerating cooling effect.

4. The improved method of dead banking a blast furnace without the necessity of including a preparatory damping charge which includes the following steps: terminating the air blast whereby the normal supp y of oxygen from the air to support combustion is removed, and promptly supplying in the lower portion of the furnace below the shaft where the normal operating temperatures are above 900 0., about the reactive point of carbon'dioxide gas in the presence of red hot carbon, an atmosphere including a gas incapable of supporting combustion, in the absence of free oxygen, whereby further combustion and ash for- 'mation is precluded, said gaseous atmosphere including substantial amounts of combustion asphyxiating gases including carbon dioxide capable of reacting endothermically with the hot coke at temperatures above 900 capable of reacting endothermically with metallic presence of hot coke in C., and also iron by an oxidizing type of reaction below 900 C., said gaseous atmosphere also including a substantial amount of carbon monoxide capable of reacting endothermically at temperatures below 900 C. with metallic iron, all of which endothermic heat absorbing type of reactions, in the absence of uncombined oxygen, contribute to effect a relatively rapid and accelerated cooling of the furnace to a temperature below the ignition point of the coke.

LAWRENCE E. RIDDLE. 

